Hillary Clinton is so far ahead of Donald Trump in the race for the presidency that she no longer even feels the need to pay attention to the Republican nominee.

Buoyed by a double-digit lead in some national polls, Mrs Clinton has said she is now looking past Mr Trump entirely, and will no longer counter allegations made by her rival.

GOP candidate Donald Trump removes his hat to fix his hair at the end of a campaign rally in Naples, Florida, also on Sunday Photo: Jonathan Ernst/Reuters

"I don't even think about responding to him anymore," Mrs Clinton said when asked about Mr Trump's charge that American media outlets are in cahoots with her presidential campaign.

"He can say whatever he wants to. He can run his campaign however he wants to, he can go off on tangents, he can go to Gettysburg and say he's gonna sue women who've made accusations against him," she added, referring to a speech given by Mr Trump the previous day.

"I'm going to keep talking about what we want to do."

A top adviser to Mr Trump acknowledged on Sunday the Republican presidential candidate was lagging behind his rival.

Kellyanne Conway, Mr Trump's campaign manager, said Mrs Clinton had "tremendous advantages," including a large campaign war chest that had allowed her to spend millions on television ads.

"We are behind," Ms Conway said on NBC's 'Meet the Press'. But she added the Trump campaign was looking to sway undecided voters not ready to support Clinton.

She also insisted Mr Trump could still win.

"The fact is that this race is not over," Ms Conway said. "He's not - we're not giving up. We know we can win this."

With only 16 days until the election, two separate polls have given Mrs Clinton a 12-point lead over Mr Trump, with the real estate mogul's support tanking among key voter groups.

An ABC News/'Washington Post' poll corroborated the findings of a study published by the Monmouth University Polling Institute which showed Mrs Clinton leading Mr Trump 50pc to 38pc in a four-way contest with two minor party candidates.

Mrs Clinton's long-held advantage with women has increased to 20 points following allegations that Mr Trump sexually harassed multiple women, according to the most recent ABC/'Washington Post' poll.

The study also suggested the former first lady was leading for the first time among men, although the four-point advantage was within the margin of error. However, Robby Mook, Mrs Clinton's campaign manager, said he was "not taking anything for granted".

But sources inside the operation have said Clinton strategists are quietly considering the possibility of a landslide victory.

In a sign of that confidence, Mrs Clinton told journalists this week that her campaign was shifting its attention to trying to take back control of a Republican majority congress, by helping Democratic politicians get elected in state races.

"We're going to be emphasising the importance of electing Democrats down the ballot,' Mrs Clinton said.

The Clinton campaign is, for example, pouring $1m (€920,000) of its funds into Indiana and Missouri. This is not because Mrs Clinton believes she can carry these reliably Republican states at the presidential level, but because she hopes it will help Democrats win senate and governor's races there.

The strategy has even been embraced by Barack Obama.

Already a key ally of Mrs Clinton, the US president will now also intervene in the state senate races, endorsing approximately 150 candidates across 20 states, according to Politico, the American political news site.

The endorsements, which will come along with a variety of robocalls, social media, mailers, and photos of Mr Obama with the candidates, represent the most involvement in down-ballot races by any president in living memory.